Arc lamp with fuse wire and biasing support means therefor



c E. RICH 1 3,515,926

. June 2, 1970 I v ARC LAMP WITH'FUSE WIRE AND BIASING "surroa'r MEANS THEREEOR Filed Feb. 12, 1968 I I 30 3| 32 33 4o 34 35 FIG. I

FIG. 2

FIG. 3

Charle E.Rich,

United States Patent 3,515,926 ARC LAMP WITH FUSE WIRE AND BIASING SUPPORT MEANS THEREFOR Charles E. Rich, Gainesville, Fla., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Feb. 12, 1968, Ser. No. 704,666 Int. Cl. H01j 1/18, 17/04 U.S. Cl. 313-146 9 Claims ABSTRACT OF THE DISCLOSURE An arc lamp structure for short-arc gas lamps with reduced susceptibility to shock and vibration damage. The structure includes an envelope enclosing a pair of coaxially aligned electrodes. A fuse wire extends across the space separating the electrodes for engagement between the electrodes. An are between the electrodes is established when the fuse wire disintegrates. The fuse wire is supported in a small indentation in either or both electrodes. One of the electrodes is spring loaded and exerts a pressure to hold the fuse in place.

BACKGROUND OF THE INVENTION There is an increasing demand for high pressure light sources with evry high power ratings, for infrared lighting systems, information display systems, and for other uses such as in laboratory tests. Arc lamp performing these functions are subject to damage through tube explosions, and shortened tube life is a result from explosions and various other causes. Extremely high temperatures result in bonding failures or failures of the envelope during operation. Stress between bonded components while the tube is operating also increase the danger from susceptance to shock and vibration.

The present means for attachment of the fuse wire element to the electrodes of such a short-arc lamp has been found lacking in some respect-s, particularly with regard to tolerance of environmental shock and vibration. One method of attaching a fuse wire to the electrode is that of welding a small diameter molybdenum wire on the major diameter of the electrode tip. The wire is laid into a shallow groove along the tapered tip and crosses the short gap between electrodes as near as possible to the center-line axis common to both electrodes.

This prior art method involves a somewhat longer piece of wire because of the point of attachment. Some of this extra length is necessary to accommodate axial length variations due to temperature changes; however, such extra length makes the assembly more susceptible to shock and vibration.

SUMMARY OF THE INVENTION The apparatus of the present invention is an arc lamp structure which includes the axial loading of a short, straight length of fuse wire secured between a pair of coaxially aligned electrode tips. Both ends of the fuse wire may rest in a small indentation in the electrodes tips to restrict lateral motion, or one end may rest in an indentation in one electrode tip while the other end is attached to the other electrode tip. The assembly is held in place by the axial compression exerted by a compression spring on one of the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational, sectional view of the arc tube electrode structure.

FIG. 2 is a sectional view of the electrode tips and fuse wire.

FIG. 3 is a sectional view of an axially movable electrode structure.

Patented June 2, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENT A first embodiment of the arc lamp, as. shown in FIG. 1, includes an envelope structure 11, an electrode 10, a fuse wire 14, an electrode 20, and a compressionspring assembly 30. Electrode 20 is comprised of a tip portion 19 having an end shaft portion 21 connected thereto by a compression spring assembly 30. Fuse wire 14 is butt welded to tip 12 of electrode 10 and extends across the shortest gap between electrodes to rest in an indentation 16 in the tip 19 of electrode 20.

Compression spring assembly 30 includes a housing 31 enclosing a cylindrical chamber 33 having a spring 32 carried therein, between electrode tip portion 19 and shaft portion 21. Spring 32 forms a mid-part of the shaft of electrode 20. A pair of spaced circular stops 34 and 36 extend inwardly from the inner surface of housing 31 to form a groove 35 within an open end of the assembly. A flange 38 on electrode shaft 21 is inserted in groove 35. Circular stop 36 is removable and is attached to housing 31 by four evenly spaced bolts 37.

Spring 32, compressed between a closed end 39 of the cylinder and stop 34, is attached to an end 40 of electrode shaft portion 21 which extends into the chamber beyond or even with stop 34. Movement of the cylindrical housing 31 coaxially with shaft 20 in either direction is limited to a given short distance by flange 38 contacting stops 34 or 36, depending on the direction of the movement.

The assembled arc lamp, without fuse wire 14, has electrodes 10 and 20 coaxially disposed with a gap between the electrode tips. Compression spring 32 is in a state of least compression, exerting a force at shaft end 40 which maintains flange 38 in contact with stop 36. Fuse wire 14, when inserted between the tips of elec trodes 10 and 20, is of such length as to require the additional compression of spring 32. Spring 32, acting through the tip portion 19 of electrode 20, exerts a force on fuse wire 14 thereby holding the fuse wire in place. When fuse wire 14 is inserted between electrodes, the compression of spring 32 will cause shaft flange 38 to break contact with stop 36. Compression spring 32 is in a state of maximum compression when shaft flange 38 is in contact with stop 34, and the maximum desirable fuse wire length is that length equivalent to the distance between electrode tips plus the distance flange 38 can travel between stops 34 and 36.

It is important that the fuse wire 14 be straight and the ends concentric and set uniformly in th small indentation in tip 16 of electrode 20 to avoid lateral thrust which would increase the bending moment of the fuse wire.

When the are lamp is activated, the fuse wire will blow as an arc is established between the electrodes. After the fuse wire blows, electrode 20 will move toward electrode 10 until flange 38 comes to rest on stop 36. During this instant the current path is maintained through spring 32.

A second embodiment, as shown in FIG. 2, includes the fuse wire inserted in indentations on both electrodes rather than welding one end of the wire, thereby eliminating the ditficult task of fusing refractory metals in a weld. Therefore, fuse wire 14 has one end inserted in an indentation in a tip 18 of electrode 10 and the other end inserted in tip 16 of electrode 20. All other structure is as previously disclosed.

A third embodiment of the arc lamp, as shown in FIG. 3, includes a variation in the structure of electrode 20 and compression spring assembly 30. Electrode 20 is a solid cylindrical shaft that projects through spring assembly 30. Spring assembly 30 includes a cylindrical housing 49 en- 3 closing a chamber 50 having a compression spring 42 and a pair of circular stops 44 and 46 which form a groove 47 within one end of chamber 50. A flange 48 on the electrode 20 shaft is inserted in groove 47. Spring 42 encircles shaft 20 and is held in a state of compression, having one end forced against wall 52 of chamber 50, the other end forced against stop 44, and a point 54 attached to the shaft 20. Housing 49 is fixed relative to both electrodes and electrode 20 can move axially in either direction being limited by flange 48 contacting stops 44 or 46, depending on the direction of movement.

Without fuse wire 14 between the tips of the electrodes and 20, compression spring 42 is in a state of least compression, and flange 48 is in contact with stop 44. Point 54 is in a state of equilibrium having equal forces applied from both sides. Fuse wire 14, when inserted be tween the tips of electrodes 10 and 20, is of such length as to require the additional compression of a portion of spring 42, causing the forces on point 54 to become unbalanced "With the maximum force being between point 54 and stop 44. Spring 42, acting through the shaft of electrode 20, exerts this force on fuse wire 14, thereby holding the fuse wire in place. When fuse wire.14 is inserted between the electrodes, shaft flange 48 breaks contact with stop 34 and may be placed in contact with stop 36 thereby placing the maximum possible unbalanced force on spring 42.

The fuse Wire will blow when the arc lamp is activated and an arc is then established between electrodes. After fuse wire 14 blows, electrode will movetoward electrode 10 until flange 48 comes to rest on stop 44. During this instant the current path remains in or through electrode 20.

I claim:

1. An arc lamp structure comprising: an envelope; first and second electrodes within said envelope in coaxially aligned spaced relation; said first and second electrodes having conical tips facing one toward the other; said second electrode including a tip portion and a shaft portion; a fuse wire secured between said electrode tips for initiating current flow between said electrodes; and biasing means carried intermediate said tip and shaft portions for securing said tip and shaft portions together in biased relationship, for electrical continuity therebetween and for retention of said fuse wire between said tips in biased relation therebetween.

2. An arc lamp as set forth in claim 1, further comprising a small indentation in the tip of said second electrode, means attaching said fuse wire at one end to the tip of said first electrode, and wherein the other end of said fuse wire rests in said small indentation.

3. An arc lamp as set forth in claim 2 wherein said biasing means includes a compression spring assembly forming a mid-part of said second electrode, means fixedly attaching a first end of said spring assembly coaxially with said tip portion of said second electrode, means flexibly attaching a second end of said spring assembly coaxially with said shaft portion of said electrode.

4. An arc lamp as set forth in claim 3, wherein said compression spring assembly includes a housing enclosing a cylindrical chamber, a cylindrical compression spring carried within said chamber and secured intermediate said tip portion and said shaft portion of said second electrode, a pair of spaced circular stops forming a groove within said chamber at said second end of the spring assembly; and further comprising a circular flange attached to said second electrode shaft portion and confined within said groove thereby allowing only limited axial movement of said housing with respect to said flange.

5. An arc lamp as set forth in claim 4 wherein said compression spring is provided with a first end in contact with said first end of said assembly housing and a second end in fixed contact with said second end of said electrode shaft portion.

6. An arc lamp as set forth in claim 5 wherein said fuse wire is straight with concentric ends and whereby insertion of the fuse wire between said electrodes compresses said spring, thereby causing an axial compression to be exerted on the fuse wire by said compression spring for retention of said wire between said tips of said electrodes.

7. An arc lamp structure comprising: an envelope; first and second electrodes within said envelope in coaxially aligned spaced relation; said first and second electrodes having conical tips facing one toward the other; a straight fuse wire having concentric ends secured between said electrode tips for initiating current flow between said electrodes; said electrode tips each having a small indentation therein for receiving said fuse wire; and biasing means for retention of said fuse wire between said tips in biased relation therebetween, said biasing means including a compression spring assembly coaxially aligned with said second electrode, and means attaching said spring assembly to said second electrode.

8. An a rc lamp as set forth in claim 7 wherein said second electrode is provided with a tip portion and a shaft portion, said spring assembly forming a tmid-part of said second electrode; said spring assembly further comprising a housing having a first end thereof fixedly attached co axially with said tip portion of said second electrode, said housing enclosing a cylindrical chamber, a compression spring within said chamber coaxially aligned with and forming a mid-part of said second electrode, and a pair of spaced circular stops forming a groove within said chamber at a second end of said housing; a circular flange attached to said electrode shaft portion and confined within said groove thereby allowing limited axial movement of said flange between said stops; and said compression spring having a first end in engagement with said first end of said housing and a second end secured to said electrode shaft portion at said second end of the housing, and whereby insertion of the fuse wire between the electrodes compresses said spring causing, thereby, an axial compression to be exerted on the fuse wire by said compression spring to hold said wire in position.

9. An arc lamp as set forth in claim 7 wherein said compression spring assembly includes a housing enclosing a cylindrical chamber, first and second circular stops forming a groove within said chamber at a first end of the housing, and a coiled compression spring coaxially aligned within said chamber in a state of longitudinal compression having a first end in contact with a second end of said chamber housing and a second end thereof abutting said first circular stop; said compression spring assembly chamber encloses a mid-portion of said second electrode and said spring encircles said shaft within the chamber; and further comprising a flange forming an integral part of said second electrode mid-portion, means attaching a mid-point of said spring to said electrode being moveable axially :with the electrode; and wherein said flange is confined within said chamber groove, having axial movement confined only by said circular stops.

References Cited UNITED STATES PATENTS 3,256,459 6/1966 Keller et al. 3l3l84 X 3,274,427 9/1966 Paquette et al. 313-184 X 3,377,497 4/1968 Keller 3*13 4 JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner US. Cl. X.R. 313-484, 217, 269 

